grpc: use pointers for load_balancing::WeakSubchannel hash/eq operations (#2439)

This is an old change that I found in my client that never got pushed
upstream, but is worth having.

Upgrading weak to owned before performing these operations is more
expensive. Just using the pointer is simpler and quicker and equally
valid.

Author: dfawley

grpc/src/client/load_balancing/mod.rs

@@ -31,6 +31,7 @@ use std::{
     fmt::{Debug, Display},
     hash::{Hash, Hasher},
     ops::{Add, Sub},
+    ptr::addr_eq,
     sync::{
         atomic::{AtomicI64, Ordering::Relaxed},
         Arc, Mutex, Weak,
@@ -456,21 +457,13 @@ impl WeakSubchannel {
 
 impl Hash for WeakSubchannel {
     fn hash<H: Hasher>(&self, state: &mut H) {
-        if let Some(strong) = self.upgrade() {
-            return strong.dyn_hash(&mut Box::new(state as &mut dyn Hasher));
-        }
-        panic!("WeakSubchannel is not valid");
+        (self.0.as_ptr() as *const () as usize).hash(state);
     }
 }
 
 impl PartialEq for WeakSubchannel {
     fn eq(&self, other: &Self) -> bool {
-        if let Some(strong_self) = self.upgrade() {
-            if let Some(strong_other) = other.upgrade() {
-                return strong_self.dyn_eq(&Box::new(&strong_other as &dyn Any));
-            }
-        }
-        false
+        addr_eq(self.0.as_ptr(), other.0.as_ptr())
     }
 }